The Ruthless Pursuit of Horsepower

Step By Step

Ever seen the inside of an LS6? You can just see the camshaft, down in the valley between the cylinder banks. Changes to the cams lift height and lobe ramp angles account for most of the new engines power gains. The valvesprings were revised, too, to accommodate the cams more aggressive profiles.

You can see how the entrance to the new air cleaner housing (on the left) has been enlarged for increased airflow. Its a simple alteration, but GM engineers had to be careful to retain the housings water-intrusion protection.

Another fairly simple change was the removal of the mass airflow sensors honeycomb grille (as seen on last years MAF on the left) to ease flow into the sensor. Engineers thought they wanted the turbulence that the grille created, but it proved to be a restriction that cost power.

Though they look like last years forged-aluminum wheels, Z06 wheels for 2002 are cast-spun aluminum. This shaves some weight from the wheels and also solves a supply problem that was constraining Z06 production.

This chart compares horsepower and torque curves for the 2001 and 2002 LS6 engines. Note that the curve shapes havent changed; the power peaks arrive at the same rpm as before. Corvette team engineers were proud of the fact that they were able to find more horsepower without sacrificing low-end torque.

From the outside, theres just one small design detail that differentiates last years Z06 from the new model. But what a difference it is. An addition to the Z06 fender badges now reads 405 HP.

Yes, the 400hp mark has been breached. Improvements to the LS6 V-8 have pushed peak horsepower from 385 to 405 and boosted peak torque from 385 lb-ft to 400. The latest iteration of the venerable pushrod small-block now makes as much horsepower as the fabled four-cam LT5 motor in the ZR-1 of the 90s. And they said it couldnt be done.

I think this tells you there is more than one way you can design an engine to achieve power, said Sam Winegarden, chief engineer for GM Powertrains small-block team. John Juriga [assistant chief engineer] and his team have done a really nice job with what you could call the ruthless pursuit of horsepower. Conventional wisdom will tell you that you need a four-valve, overhead-cam arrangement, and that is simply not the case. You can make it work either way. The pushrod small-block has a bright future, and theres more where that came from.

Juriga and his team achieved the power gains the old-fashioned way, by improving the flow of air into and out of the engine. And we were able to get these increases with no sacrifice in low-end torque, Juriga explained. We kept the horsepower and torque peaks at the same rpm levels. So the Z06s basic driving character hasnt changed. You just get extra oomph at the right spot in the rev rangeoomph that translates into quicker acceleration. GMs testing showed the Z06s 0-60 time dropping from 4.0 to 3.9 seconds, and its quarter-mile e.t. going from 12.6 to 12.4 seconds.

The changes to the LS6 start up front with the air-cleaner housing. Its opening was enlarged by more than 6 cubic inches to allow more air into the unit. The alteration sounds simple, but Juriga explained it had to be done carefully so as not to compromise the housings water intrusion protection. Downstream of the housing, the mass airflow (MAF) sensor was modified by removing its pre-sensor honeycomb grille to smooth flow into the intake manifold.

The manifold and cylinder heads are carryover items, but modifications to the camshaft and valvetrain are credited with making the largest contributions to the power boost. The cam lobes were altered for more liftfrom 13.3 mm to 14 mmand the profiles changed to open the valves more quickly (though the events duration remains the same). To compensate for the more aggressive cam profiles, the valvesprings were revised with higher seat loads. At the same time, the valves themselves were redesigned. This redesign also gave the engineers the opportunity to improve heat transfer from the exhaust valves to the valve guides by filling the hollow stems with a liquid sodium alloy.

Raising the exhaust valve lift was just the first step in improving waste-gas flow out of the LS6. The eliminated pup catalytic converters, located just downstream from the exhaust manifolds, took a big restriction out of the exhaust system. The under-floor converters were correspondingly modified to make up for the loss of the pre-converters, and they are efficient enough to retain the Z06s NLEV (national low-emission vehicle) status. Also retained is the Z06s 19-mpg city/28-mpg highway fuel economy rating.

And true to the cars sporting nature, you still cannot get an automatic transmission for the Z06. You have to be willing to use a clutch and stir the cars six-speed shifter to drive the ultimate Corvette.

Not all the improvements to the 02 Z06 are engine-related. Suspension tweaks include new valving in the rear shocks to better plant the tires and transfer power to the ground. The revalved dampers also give the Z06 a more civilized ride, according to Chief Corvette Engineer Dave Hill. In an effort to reduce mass, the front stabilizer-bar links were redesigned in cast aluminum, rather than rolled-rod steel; and the wheels are now cast-spun aluminum as opposed to forged, which shaves 1.3 pounds from the cars weight.

Changing the wheels also opened a production bottleneck Chevrolet had with last years Z06, Hill said. They had trouble getting enough of the forged wheels from their supplier, so volume was lower than they anticipated. With the new cast-spun wheels, that problem is solved for 02, according to Hill.

So how do all the improvements work when youre behind the wheel? Well, while we cant argue with the idea that more power is a good thing, wed need more seat time to truly sort out the differences between the two models. Last years Z06 was already a mighty machine, and you have to be pretty sensitive to the caror driving it at or near 10/10thsto feel what amounts to a five percent horsepower increase and a three percent bump in peak torque. And how many of us are really quick enough and consistent enough with the shift lever to feel a tenth of a second drop in 0-60 times?

Of course, the driver who pilots his Corvette at or near 10/10ths is a prime target for the Z06. The car is really aimed at the extreme performance enthusiast, said Hill, which is probably less than a quarter of our customers. These are the people who could care less about having a removable roof or an automatic transmission.

Hill recounted the genesis of the Z06, how the hardtop body style was rescued from the poorly conceived idea of offering it as a value model of the Corvette. At the last minute we decided to put Z51 pieces in those cars. But our team also wanted to build a high-performance car using the hardtops attributes of light weight and stiffness. Not just with a hot engine, but a total package with power and handling. It would be the kind of Corvette that the engineers would want. And so the Z06 was born.

And the improvements wont stop here. When Juriga was asked if the team considered enlarging the LS6s displacement as part of the 02 engine tweaks, his hesitation before answering spoke volumes. His eventual reply, When we first designed the engine we did so with future improvements in mind, said a lot without saying more than public relations folks nearby would allow. But that statement, coupled with Winegardens more where that came from comment, lead us to believe that GM is already mining the LS6s untapped potential.

As do a couple of important milestones. Corvettes 50th anniversary is in 2003, and the factory is planning a year-long celebration, complete with special edition cars, starting in July 2002less than a year from now. And dont forget our friends in the Viper camp have already announced that the engine in the 2003 RT/10 will put out 500 hp and 500 lb-ft of torque. Sounds like a challenge to us.

xclose

The Z06 Gets Even Stronger For 2002

The mighty LS6, with its trademark red covers, is even mightier for 2002 with more horsepower and torque.

Ever seen the inside of an LS6? You can just see the camshaft, down in the valley between the cylinder banks. Changes to the cams lift height and lobe ramp angles account for most of the new engines power gains. The valvesprings were revised, too, to accommodate the cams more aggressive profiles.

You can see how the entrance to the new air cleaner housing (on the left) has been enlarged for increased airflow. Its a simple alteration, but GM engineers had to be careful to retain the housings water-intrusion protection.

Another fairly simple change was the removal of the mass airflow sensors honeycomb grille (as seen on last years MAF on the left) to ease flow into the sensor. Engineers thought they wanted the turbulence that the grille created, but it proved to be a restriction that cost power.

Though they look like last years forged-aluminum wheels, Z06 wheels for 2002 are cast-spun aluminum. This shaves some weight from the wheels and also solves a supply problem that was constraining Z06 production.

This chart compares horsepower and torque curves for the 2001 and 2002 LS6 engines. Note that the curve shapes havent changed; the power peaks arrive at the same rpm as before. Corvette team engineers were proud of the fact that they were able to find more horsepower without sacrificing low-end torque.